A color filter is produced by preparing a colored photosensitive composition containing a pigment-dispersed composition in which an organic pigment or an inorganic pigment is dispersed, a polyfunctional monomer, a polymerization initiator, an alkali-soluble resin, and other components, and forming a colored pattern by using the composition according to a photolithography method or an ink jet method.
In recent years, there is a trend for applications of color filters used in liquid crystal display devices (LCDs) to expand beyond monitors towards television (TVs). With this trend towards expanded applications, the color filters are desired to have high color quality with respect to chromaticity, and contrast. Similarly, color filters used in image sensors (solid-state image pickup devices) have begun to be desired to have high color quality such as reduced color unevenness and improved color resolution.
In order to satisfy the desires, the pigment contained in the colored photosensitive composition or the photocurable composition is desired to be dispersed in a finer state (improved dispersibility), and in stable state (improved dispersion stability). When dispersibility of the pigment is insufficient, problems arise in that colored pixels formed by a photolithographic method has a fringe (serration at an edge) or surface irregularities, the amount of residual matter (residue) remaining after development on the substrate is large, the chromaticity or dimensional precision of a manufactured color filter is thus reduced, and contrast thereof is remarkably deteriorated. In a case in which the dispersion stability of the pigment is insufficient, problems tend to arise in a production process of the color filter particularly in that uniformity of film thickness in a coating process of the colored photosensitive composition or the photocurable composition decreases, sensitivity at an light exposure process decreases, or alkali solubility in a development process decreases. Furthermore, in a case in which the dispersion stability of the pigment is poor, there is a problem in that components of the colored photosensitive composition aggregate and raise the viscosity with time, which leads to an extremely short pot-life. In order to solve such problems, a polymer-type pigment dispersant in which an organic dye structure and a polymer are bonded to each other, for example, is presented (refer to Japanese Patent Application Laid-Open (JP-A) No. 2008-009426). Although fine-sized pigment particles are effective in improving color properties, such as contrast, of a color filter, the fine diameter of the pigment particles leads to an increase in the surface area of the pigment particles, increases aggregation force between pigment particles, and often makes it difficult to achieve both of dispersibility and dispersion stability at high levels.
The following techniques for fining pigment particles are known.
In general, a method whereby a pigment, a water-soluble inorganic salt, and a water-soluble organic solvent which does not substantially dissolve the inorganic salt are mechanically kneaded by using a kneader or the like (salt milling method) is commonly known as a method for fining primary particles of a pigment. The resultant mixture containing fine pigment primary particles is added to water, and agitated using a mixer or the like to form a slurry. Next, the slurry is filtered, washed with water, and dried, as a result of which a fine pigment in the form of a secondary aggregate, which is an aggregate of the pigment primary particles, is obtained. A dispersing process using an ordinary dispersing machine such as a sand mill or a ball mill is a process whereby the secondary aggregate, which is an aggregate of the pigment primary particles, are crumbled to obtain a dispersion in a state close to a primary particle state.
Although fine pigment primary particles are obtained by, for example, the above method, various pigment dispersants have been developed in order to enhance the dispersibility and dispersion stability of the primary particles.
Among pigment dispersants, for example, a ω-carboxypolycaprolactone monomethacrylate copolymer is proposed in JP-A No. 2004-287409 for obtaining high-resolution pixels, the copolymer having favorable alkali-developability.
In addition, JP-A No. 2003-238837, for example, proposes a high-molecular compound which has a polymer structure of a vinyl compound such as styrene or an alkyl(meth)acrylate as a graft chain, and which further has a heterocyclic structure at a side chain, for the purpose of improving dispersibility and alkali-developability.
However, these methods are still insufficient for addressing market's demands for further improved contrast, and fine pigments are desired to have still higher dispersibility and dispersion stability.
In the production of a color filter using a photocurable composition containing a pigment-dispersed composition, the photocurable composition is applied to and dried on a substrate or a substrate on which a light-shielding layer of a desired pattern has been formed in advance, and the resultant dry coating film is thereafter irradiated with a radiation (hereinafter referred to as “light exposure”) in a desired pattern and developed to obtain pixels of each color.
However, a color filter thus produced has a problem in that residue and background staining tend to be generated on the substrate or light-shielding layer at regions that have not exposed to light during the development process, and pixels that have been post-baked after development have inferior film coating properties, such as inferior surface smoothness. Moreover, the degree of the residue, background staining, and surface smoothness deterioration on the substrate or the light-shielding layer tend to be more remarkable as the concentration of the pigment contained in the photocurable composition increases. Therefore, it has been difficult to achieve sufficient color density with conventional photocurable compositions for color filters.
Moreover, a pigment-dispersed composition is known (refer to Japanese Patent No. 3094403 and JP-A No. 2004-287409) in which a block-type, random-type, or linear high-molecular compound to which acrylic acid is introduced is used as an alkali-soluble resin for the purpose of imparting an alkali-developability. However, this is still insufficient to achieve both of dispersibility of the pigment and developability when applied to a curable composition for forming a pattern of a color filter or the like.
Furthermore, with an increase in the size of the substrate in recent years, a slit coating method is studied as a coating method. In comparison with conventional spin coating, slit coating has advantages in that slit coating provides excellent thickness uniformity of the coating film and reduces wasted coating liquid.
However, with slit coating, a coating liquid is exposed to the outside air at the slit aperture of the head tip, and thus drying or solidification of the coating liquid (photocurable composition) occurs easily at the head tip. The solidified coating liquid causes clogging of the slit nozzle and longitudinal streak unevenness of a coating film coated on a transparent substrate (coating streak along the coating direction).
In addition, the solidified coating liquid detaches from the head tip portion, and causes decrease of coating quality such as incorporation as unwanted matter into an applied coating film. In order to avoid this, it is requested that dried or precipitated photocurable composition properties such that it dissolves rapidly when contacting with a coating liquid (hereinafter referred to as “dry film redissolvability”).
In order to ameliorate these problems, a method in which a surfactant or a dispersant such as a resinous dispersant is used is known (for example, refer to JP-A No. 2003-294935 and JP-A No. 2001-164142). However, use of these dispersants causes problems such as reduction in the strength of a coating film, reduction in developability, reduction in the adhesiveness to a substrate such as glass, and reduction in durability. Furthermore, it has been difficult to achieve both of excellence in dispersion stability of a photocurable composition and dry film redissolvability of a coating liquid, and provision of strong adhesiveness between a coating film and a substrate such as glass.
In addition, a color filter is required to have high color density as the film is made thinner in recent years. In order to form a color filter having high color density, the concentration of colorant used in a colored resin composition to be used needs to be increased. However, a problem arises in that components contributing to image formation properties such as solubility in an alkali developer liquid relatively decrease, and the originally possessed image formation properties are lost. In order to solve such problems, use of a dispersant having both a dispersing function and a binder function has been tried aiming at maintaining image formation properties while maintaining a high colorant concentration. Furthermore, a pigment-dispersed composition in which a linear high-molecular compound of block-type, random-type, or the like having acrylic acid introduced thereto is used as an alkali-soluble resin is known (refer to JP-A No. 2004-287409). However, sufficient dispersibility has not yet been achieved, particularly in the case of extremely fine pigments.